From VMS to Linux HOWTO

This HOWTO is aimed at all those who have been using VMS and now need or
want to switch to Linux, the free UNIX clone. The transition is made
(hopefully) painless with a step--to--step comparison between commands and
available tools.

1. Introduction

1.1. Why Linux?

You've heard that UNIX is difficult and balk at the prospect of leaving VMS,
don't you? Don't worry. Linux, one of the finest UNIX clones, is not more
difficult to use than VMS; actually, I find it easier. Although VMS
aficionados may not agree, in many people's opinion Linux is much more
powerful and versatile.

Linux and VMS are both good operating systems and accomplish essentially the
same tasks, but Linux has a few features that make it a good alternative to
VMS. Moreover, Linux is available for PCs while VMS is not, and modern
Pentium-based Linux machines can outperform a VAX. The icing on the cake is
the excellent performance of modern video cards, which turn an X11-based
Linux box into a fast graphic workstation; nearly always, quicker than
dedicated machines.

I imagine you're a university researcher or a student, and that you use
VMS for the following everyday tasks:

writing papers with TeX/LaTeX;

programming in Fortran;

doing some graphics;

using Internet services;

et cetera.

In the following sections I'm going to explain to you how to do these
tasks under Linux, exploiting your experience with VMS. Prerequisites:

Linux and X Window System are properly installed;

there's a system administrator to take care of the technical
details (please get help from them, not from me ;-) ;

your shell---the equivalent of DCL---is bash (ask your
sysadm).

Please note that this HOWTO is not enough to acquaint you fully with
Linux: it only contains the bare essential to get you started. You
should learn more about Linux to make the most of it (advanced bash
features, programming, regular expressions...). From now on, RMP means
`please read the man pages for further details'. The man pages are the
equivalent of the command HELP.

The Linux Documentation Project documents, available on �, are an important source of
information. I suggest that you read Larry Greenfield's ``Linux User
Guide''---it's invaluable for the novice user.

And now, go ahead.

1.2. Comparing Commands and Files

This table attempts to compare VMS' and Linux' most used commands. Please
keep in mind that the syntax is often very different; for more details,
refer to the following sections.

But of course it's not only a matter of different command names. Read on.

2. Short Intro

This is what you absolutely need to know before logging in the first
time. Relax, it's not much.

2.1. Files

Under VMS filenames are in the form filename.extension;version.
Under Linux, the version number doesn't exist (big limitation, but see
Section Section 10.2); the filename
has normally a limit of 255 characters and can have as many dots as you
like. Example of filename: This.is_a_FILEname.txt.

Linux distinguishes between upper case and lower case characters:
FILENAME.txt and filename.txt are two different files;
ls is a command, LS is not.

A filename starting with a dot is a `hidden' file (that is,
it won't normally show up in dir listings), while filenames ending with a
tilde '˜' represent backup files.

For other examples involving directories, see below; for details about
protections, ownership, and advanced topics, see Section Section 8.

2.2. Directories

Within the same node and device, directories names under VMS are in
the form [top.dir.subdir]; under Linux, /top/dir/subdir/. On
the top of the directory tree lies the so--called `root directory' called
/; underneath there are other directories like /bin,
/usr, /tmp, /etc, and others.

The directory /home contains the so--called users' `home
directories': e.g. /home/guido, /home/warner, and so on.
When a user logs in, they start working in their home dir; it's the
equivalent of SYS$LOGIN. There's a shortcut for the home
directory: the tilde '˜'. So, cd ˜/tmp is the same
as, say, cd /home/guido/tmp.

Directory names follow the same rules as file names. Furthermore,
each directory has two special entries: one is . and refers to the
directory itself (like []), and .. that refers to the parent
directory (like [-]).

For protections, ownership, and advanced topics, see Section Section 8.

2.3. Programs

Commands, compiled programs, and shell scripts (VMS' `command
files') don't have sort of mandatory extensions like .EXE or .COM
and can be called whatever you like. Executable files are marked by an
asterisk '*' when you issue ls -F.

To run an executable file, just type its name (no RUN
PROGRAM.EXE or @COMMAND). Caveat: it's essential that the file be
located in a directory included in the path of executables, which is a
list of directories. Typically, the path includes dirs like /bin,
/usr/bin, /usr/X11R6/bin, and others. If you write your
own programs, put them in a directory you have included in the path (see how
in Section Section 9). As an alternative,
you may run a program specifying its complete path: e.g.,
/home/guido/data/myprog; or ./myprog, if the current
directory isn't in the path.

Command switches are obtained with /OPTION= under VMS, and
with -switch or --switch under Linux, where switch is a
letter, more letters combined, or a word. In particular, the switch -R
(recursive) of many Linux commands performs the same action as [...]
under VMS;

You can issue several commands on the command line:

$ command1 ; command2 ; ... ; commandn

Most of the flexibility of Linux comes from two features awkwardly
implemented or missing in VMS: I/O redirection and piping. (I have been told
that recent versions of DCL support redirection and piping, but I don't have
that version.) Redirection is a side feature under VMS (remember
the switch /OUTPUT= of many commands), or a fastidious process,
like:

$ DEFINE /USER SYS$OUTPUT OUT
$ DEFINE /USER SYS$INPUT IN
$ RUN PROG

which has the simple Linux (UNIX) equivalent:

$ prog < in > out

Piping is not readily available under VMS, but has a key role under UNIX. A
typical example:

which means: the program myprog gets its input from the file
datafile (via <), its output is piped (via |) to
the program filter_1 that takes it as input and processes it, the
resulting output is piped again to filter_2 for further processing, the
final output is appended (via >>) to the file result.dat,
and error messages are redirected (via 2>) onto the file
errors.log. All this in background (& at the end of the
command line). More about this in Section Section 11.

2.4. Quick Tour

Now you are ready to try Linux out. Enter your login name and password
exactly as they are. For example, if your login name and password are
john and My_PassWd, don't type John or my_passwd.
Remember, UNIX distinguishes between capital and small letters.

Once you've logged in, you'll see a prompt; chances are it'll be something
like machinename:$. If you want to change the prompt or make
some programs start automatically, you'll have to edit a `hidden' file
called .profile or .bash_profile (see example in Section Section 9). This is the equivalent of
LOGIN.COM.

Pressing ALT--F1, ALT--F2, ... ALT--F6 switches between `virtual consoles'.
When one VC is busy with a full--screen application, you can flip over to
another and continue to work. Try and log in to another VC.

Now you may want to start X Window System (from now on, X). X is a graphic
environment very similar to DECWindows---actually, the latter derives from
the former. Type the command startx and wait a few seconds; most likely
you'll see an open xterm or equivalent terminal emulator, and possibly
a button bar. (It depends on how your sysadm configured your Linux box.)
Click on the desktop (try both mouse buttons) to see a menu.

While in X, to access the text mode (`console') sessions press
CTRL--ALT--F1 ... CTRL--ALT--F6. Try it. When in console, go back to X
pressing ALT--F7. To quit X, follow the menu instructions or press
CTRL--ALT--BS.

Type the following command to list your home dir contents, including the
hidden files:

$ ls -al

Press SHIFT--PAG UP to back-scroll. Now get help about the ls command
typing:

$ man ls

pressing 'q' to exit. To end the tour, type exit to quit your session.
If now you want to turn off your PC, press CTRL--ALT--DEL and wait a few
seconds (never switch off the PC while in Linux! You could damage the
filesystem.)

If you think you're ready to work, go ahead, but if I were you I'd jump
to Section Section 8.

3. Editing Files

Linux doesn't have EDT, but there are scores of editors available. The
only one that's guaranteed to be included in every UNIX version is
vi---forget it, your sysadm must have installed something better.
Probably the most popular editor is emacs, which can emulate EDT
to a certain degree; jed is another editor that provides EDT
emulation.

These two editors are particularly useful for editing program sources, since
they have two features unknown to EDT: syntax hilighting and automatic
indentation. Moreover, you can compile your programs from within the editor
(command ESC-X compile); in case of a syntax error, the cursor will be
positioned on the offending line. I bet that you'll never want to use the
true blue EDT again.

If you have emacs: start it, then type ESC-X edt-emulation-on.
Pressing ALT--X or ESC-X is emacs' way of issuing commands, like
EDT's CTRL--Z. From now on, emacs acts like EDT apart from a
few commands. Differences:

to insert a new file in a buffer, press CTRL-X CTRL-F, then
CTRL-X B to switch among buffers.

If you have jed: ask your sysadm to configure jed properly.
Emulation is already on when you start it; use the normal keypad keys, and
press CTRL--H CTRL--H or CTRL-? to get help. Commands are issued in the same
way as emacs'. In addition, there are some handy key bindings missing
in the original EDT; key bindings can also be tailored to your own
taste. Ask your sysadm.

In alternative, you may use another editor with a completely different
interface. emacs in native mode is an obvious choice; another popular
editor is joe, which can emulate other editors like emacs itself
(being even easier to use) or the DOS editor. Invoke the editor as
jmacs or jstar and press, respectively, CTRL-X H or CTRL-J to get
online help. emacs and jed are much more powerful than good
ol' EDT.

4. TeXing

TeX and LaTeX are identical to their VMS counterparts---only quicker :-),
but the tools to handle the .dvi and .ps files are superior:

to visualize a .dvi file, type within an X session:
xdvi filename.dvi &. Click on the page to magnify. This program
is smart: if you edit and run TeX producing newer versions of the .dvi
file, xdvi will update it automatically;

to visualize a .ps file, type within an X session: ghostview
filename.ps &. Click on the page to magnify. The whole document or
selected pages can be printed. A newer and better program is gv.

to print the .ps: usually the command lpr mypaper.ps will
do, but if the PostScript printer is called, say, `ps' (ask your
sysadm) you'll do: lpr -Pps mypaper.ps. For more information
about print queues, go to Section Section 8.4.

5. Programming

Programming under Linux is much better: there are lots of tools that
make programming easier and quicker. For instance, the drudgery of
editing--saving--exiting--compiling--re-editing can be cut short by using
editors like emacs or jed, as seen above.

5.1. Fortran

Not substantial differences here, but note that at the time of writing the
available (free) compilers are not 100% compatible with VMS'; expect
some minor quirks. (It's actually the VMS compiler which has non-standard
extensions.) See /usr/doc/g77/DOC or /usr/doc/f2c/f2c.ps
for details.

Your sysadm has installed a native compiler called g77 (good but, as of
version 0.5.21, still not perfectly compatible with DEC Fortran) or possibly
the Fortran to C translator, f2c, and one of the front-ends that make it
mimic a native compiler. In my experience, the package yaf77 is the
one that provides best results.

To compile a Fortran program with g77, edit the source, save it with
extension .f, then do:

$ g77 myprog.f

which creates by default an executable called a.out (you don't have
to link anything). To give the executable a different name and do some
optimisation:

$ g77 -O2 -o myprog myprog.f

Beware of optimisations! Ask your sysadm to read the documentation that
comes with the compiler and tell you if there are any problems.

To compile a subroutine:

$ g77 -c mysub.f

This creates a file mysub.o. To link this subroutine to a program,
you'll do

$ g77 -o myprog myprog.f mysub.o

If you have many external subroutines and you want to make a library, do the
following:

$ cd subroutines/
$ cat *f >mylib.f ; g77 -c mylib.f

This will create mylib.o that you can link to your programs.

Finally, to link an external library called, say, libdummy.so:

$ g77 -o myprog myprog.f -ldummy

If you have f2c, you only have to use f77 or fort77 instead
of g77.

Another useful programming tool is make, described below.

5.2. Using make

The utility make is a tool to handle the compilation of programs that
are split into several source files. The VMS counterparts are MMS
and MMK, which have a different syntax.

Let's suppose you have source files containing your routines, file_1.f,
file_2.f, file_3.f, and a source file of the main program that uses the
routines, myprog.f. If you compile your program manually, whenever you
modify one of the source files you have to figure out which file depends on
which, which file to recompile first, and so on.

Instead of getting mad, you can write a `makefile'. This is a text file
containing the dependencies between your sources: when one is modified, only
the ones that depend on the modified file will be recompiled.

Save this file as Makefile and type make to compile your program;
alternatively, save it as myprog.mak and type make -f myprog.mak.
And of course, RMP.

5.3. Shell Scripts

Shell scripts are the equivalent of VMS' command files, and allow for very
powerful constructs.

To write a script, all you have to do is write a standard ASCII file
containing the commands, save it, then make it executable with the
command chmod +x <scriptfile>. To execute it, type its name.

Writing scripts under bash is such a vast subject it would require a
book by itself, and I will not delve into the topic any further. I'll just
give you a more-or-less comprehensive and (hopefully) useful example you can
extract some basic rules from.

5.4. C

Linux is an excellent environment to program in C. Taken for granted that
you know C, here are a couple of guidelines. To compile your standard
hello.c you'll use the gcc compiler, which comes as part of Linux
and has the same syntax as g77:

$ gcc -O2 -o hello hello.c

To link a library to a program, add the switch -l<libname>.
For example, to link the math library and optimize do

When your program is made of several source files, you'll need to use the
utility make described above. Just use gcc and C source files in
the makefile.

You can invoke some help about the C functions, that are covered by man
pages, section 3; for example,

$ man 3 printf

There are lots of libraries available out there; among the first you'll want
to use are ncurses, to handle text mode effects, and svgalib, to
do graphics.

6. Graphics

Among the scores of graphic packages available, gnuplot stands out
for its power and ease of use. Go to X and type gnuplot, and have
two sample data files ready: 2D-data.dat (two data per line), and
3D-data.dat (three data per line).

Example of 3-D graphs (each `row' of X values is followed by a blank
line):

gnuplot> set parametric ; set hidden3d ; set contour
gnuplot> splot '3D-data.dat' using 1:2:3 with linespoints

A single-column datafile (e.g., a time series) can also be plotted as a 2-D
graph:

gnuplot> plot [-5:15] '2D-data-1col.dat' with linespoints

or as a 3-D graph (blank lines in the datafile, as above):

gnuplot> set noparametric ; set hidden3d
gnuplot> splot '3D-data-1col.dat' using 1 with linespoints

To print a graph: if the command to print on your Postscript printer is
lpr -Pps file.ps, issue:

gnuplot> set term post
gnuplot> set out '| lpr -Pps'
gnuplot> replot

then type set term x11 to restore. Don't get confused---the last print
will come out only when you quit gnuplot.

For more info, type help or see the examples in directory
/usr/lib/gnuplot/demos/, if you have it.

7. Mail and Internet Tools

Since Internet was born on UNIX machines, you find plenty of nice and
easy-to-use applications under Linux. Here are just some:

Mail: use elm or pine to handle your email; both
programs have on-line help. For short messages, you could use mail, as
in mail -s "hello mate" user@somewhere < msg.txt. You may like programs
like xmail or some such.

Newsgroups: use tin or slrn, both very intuitive and
self-explanatory.

ftp: apart from the usual character-based ftp, ask your
sysadm to install the full-screen ncftp or a graphical ftp client like
xftp.

WWW: the ubiquitous netscape, or xmosaic,
chimera, and arena are graphical web browsers; a character-based
one is lynx, quick and effective.

8. Advanced Topics

Here the game gets tough. Learn these features, then you'll be ready to say
that you `know something about Linux' ;-)

8.1. Permissions and Ownership

Files and directories have permissions (`protections') and ownership, just
like under VMS. If you can't run a program, or can't modify a file, or can't
access a directory, it's because you don't have the permission to do so,
and/or because the file doesn't belong to you. Let's have a look at the
following example:

$ ls -l /bin/ls
-rwxr-xr-x 1 root bin 27281 Aug 15 1995 /bin/ls*

The first field shows the permissions of the file ls (owner root,
group bin). There are three types of ownership: owner, group, and others
(similar to VMS owner, group, world), and three types of permissions:
read, write (and delete), and execute.

From left to right, - is the file type (- = ordinary file, d
= directory, l = link, etc); rwx are the permissions for the file
owner (read, write, execute); r-x are the permissions for the group of
the file owner (read, execute); r-x are the permissions for all other
users (read, execute).

To change a file's permissions:

$ chmod <whoXperm> <file>

where who is u (user, that is owner), g (group), o (other),
X is either + or -, perm is r (read), w (write), or
x (execute). Examples:

$ chmod u+x file

this sets the execute permission for the file owner. Shortcut:
chmod +x file.

$ chmod go-wx file

this removes write and execute permission for everyone except the owner.

$ chmod ugo+rwx file

this gives everyone read, write, and execute permission.

A shorter way to refer to permissions is with numbers: rwxr-xr-x can be
expressed as 755 (every letter corresponds to a bit: --- is 0,
--x is 1, -w- is 2...).

For a directory, rx means that you can cd to that directory, and
w means that you can delete a file in the directory (according to the
file's permissions, of course), or the directory itself. All this is only
part of the matter---RMP.

8.2. Multitasking: Processes and Jobs

More about running programs. There are no `batch queues' under Linux as
you're used to; multitasking is handled very differently. Again, this is
what the typical command line looks like:

$ command -s1 -s2 ... -sn par1 par2 ... parn < input > output &

where -s1, ..., -sn are the program switches,
par1, ..., parn are the program parameters.

Now let's see how multitasking works. Programs, running in foreground or
background, are called `processes'.

To launch a process in background:

$ progname [-switches] [parameters] [< input] [> output] &
[1] 234

the shell tells you what the `job number' (the first digit; see below) and
PID (Process IDentifier) of the process are. Each process is identified
by its PID.

To see how many processes there are:

$ ps -ax

This will output a list of currently running processes.

To kill a process:

$ kill <PID>

You may need to kill a process when you don't know how to quit it
the right way... ;-). Sometimes, a process will only be killed by
one of the following:

$ kill -15 <PID>
$ kill -9 <PID>

In addition to this, the shell allows you to stop or temporarily suspend a
process, send a process to background, and bring a process from background
to foreground. In this context, processes are called `jobs'.

To see how many jobs there are:

$ jobs

jobs are identified by the numbers the shell gives them, not by their PID.

To stop a process running in foreground:

$ CTRL-C

(it doesn't always work)

To suspend a process running in foreground:

$ CTRL-Z

(ditto)

To send a suspended process into background (it becomes a job):

$ bg <job>

To bring a job to foreground:

$ fg <job>

To kill a job:

$ kill <%job>

8.3. Files, Revisited

More information about files.

stdin, stdout, stderr: under UNIX, every system component is
treated as if it were a file. Commands and programs get their input from a
`file' called stdin (standard input; usually, the keyboard), put their
output on a `file' called stdout (usually, the screen), and error
messages go to a `file' called stderr (usually, the screen).
Using < and > you redirect input and output to a different
file. Moreover, >> appends the output to a file instead of
overwriting it; 2> redirects error messages (stderr); 2>&1
redirects stderr to stdout, while 1>&2 redirects stdout to stderr.
There's a `black hole' called /dev/null: everything redirected to
it disappears;

wildcards: '*' is almost the same. Usage: * matches all
files except the hidden ones; .* matches all hidden files; *.* matches
only those that have a '.' in the middle, followed by other characters;
p*r matches both `peter' and `piper'; *c* matches both `picked' and `peck'.
'%' becomes '?'. There is another wildcard: the
[]. Usage: [abc]* matches files starting with a, b, c;
*[I-N,1,2,3] matches files ending with I, J, K, L, M, N, 1, 2, 3;

# $HOME/.inputrc
# Last modified: 16 January 1997.
#
# This file is read by bash and defines key bindings to be used by the shell;
# what follows fixes the keys END, HOME, and DELETE, plus accented letters.
# For more information, man readline.
"\e[1~": beginning-of-line
"\e[3~": delete-char
"\e[4~": end-of-line
set bell-style visible
set meta-flag On
set convert-meta Off
set output-meta On
set horizontal-scroll-mode On
set show-all-if-ambiguous On
# (F1 .. F5) are "\e[[A" ... "\e[[E"
"\e[[A": "info "

10. Useful Programs

10.1. Browsing Files: less

You'll use this file browser every day, so I'll give you a couple of tips to
use it at best. First of all, ask your sysadm to configure less so as
it can display not only plain text files, but also compressed files,
archives, and so on.

Like recent versions of TYPE, less lets you browse files
in both directions. It also accepts several commands that are issued
pressing a key. The most useful are:

first of all, press q to leave the browser;

h gives you extensive help;

g to go to beginning of file, G to the end, number+g
to go to line `number' (e.g. 125g), number+% to move to that
percentage of the file;

m+letter marks current position (e.g. ma); '+letter go
to the marked position.

:e examines a new file;

!command executes the shell command.

10.2. Numbered Backups Under Linux

Alas, Linux doesn't still support file version numbers, but you overcome
this limitation in two ways. The first is to use RCS, the Revision Control
System, which allows you to keep previous versions of a file. RCS is
covered in ``The RCS MINI-HOWTO'' (�).

The second way is to use an editor that knows how to deal with numbered
backups; emacs and jed are OK. In emacs, add
these lines in your .emacs:

In jed, make sure you have version 0.98.7 or newer; the patch for
numbered backups is available on �.

10.3. Archiving: tar & gzip

Under UNIX there are some widely used applications to archive and
compress files. tar is used to make archives, that is collections of
files. To make a new archive:

$ tar -cvf <archive_name.tar> <file> [file...]

To extract files from an archive:

$ tar -xpvf <archive_name.tar> [file...]

To list the contents of an archive:

$ tar -tf <archive_name.tar> | less

Files can be compressed to save disk space using compress, which is
obsolete and shouldn't be used any more, or gzip:

$ compress <file>
$ gzip <file>

that creates a compressed file with extension .Z (compress) or .gz
(gzip). These programs don't make archives, but compress files
individually. To decompress, use:

$ compress -d <file.Z>
$ gzip -d <file.gz>

RMP.

The unarj, zip and unzip utilities are also available. Files
with extension .tar.gz or .tgz (archived with tar, then
compressed with gzip) are very common in the UNIX world. Here's how to
list the contents of a .tar.gz archive:

$ tar -ztf <file.tar.gz> | less

To extract the files from a .tar.gz archive:

$ tar -zxf <file.tar.gz>

11. Real Life Examples

UNIX' core idea is that there are many simple commands that can linked
together via piping and redirection to accomplish even really complex tasks.
Have a look at the following examples. I'll only explain the most complex
ones; for the others, please study the above sections and the man pages.

Problem: ls is too quick and the file names fly away.

Solution:

$ ls | less

Problem: I have a file containing a list of words. I want to sort it
in reverse order and print it.

Solution:

$ cat myfile.txt | sort -r | lpr

Problem: my data file has some repeated lines! How do I get rid of them?

Solution:

$ sort datafile.dat | uniq > newfile.dat

Problem: I have a file called 'mypaper.txt' or 'mypaper.tex' or some
such somewhere, but I don't remember where I put it. How do I find it?

Solution:

$ find ~ -name "mypaper*"

Explanation: find is a very useful command that lists all the files
in a directory tree (starting from ˜ in this case). Its output
can be filtered to meet several criteria, such as -name.

Problem: I have a text file containing the word 'entropy' in this
directory, is there anything like SEARCH?

Solution: yes, try

$ grep -l 'entropy' *

Problem: somewhere I have text files containing the word 'entropy', I'd
like to know which and where they are. Under VMS I'd use search entropy
[...]*.*;*, but grep can't recurse subdirectories. Now what?

Solution:

$ find . -exec grep -l "entropy" {} \; 2> /dev/null

Explanation: find . outputs all the file names starting from the
current directory, -exec grep -l "entropy" is an action to be
performed on each file (represented by {}), \
terminates the command. If you think this syntax is awful, you're right.

Explanation: grep works like search, and combining it with
find we get the best of both worlds.

Problem: I have a data file that has two header lines, then every
line has 'n' data, not necessarily equally spaced. I want the 2nd and
5th data value of each line. Shall I write a Fortran program...?

Solution: nope. This is quicker:

$ awk 'NL > 2 {print $2, "\t", $5}' datafile.dat > newfile.dat

Explanation: the command awk is actually a programming language:
for each line starting from the third in datafile.dat, print out
the second and fifth field, separated by a tab. Learn some awk---it
saves a lot of time.

Problem: I've downloaded an FTP site's ls-lR.gz to check its
contents. For each subdirectory, it contains a line that reads "total xxxx",
where xxxx is size in kbytes of the dir contents. I'd like to get the grand
total of all these xxxx values.

Problem: I've written a Fortran program, myprog, to calculate a
parameter from a data file. I'd like to run it on hundreds of data files
and have a list of the results, but it's a nuisance to ask each time for
the file name. Under VMS I'd write a lengthy command file, and under Linux?

Solution: a very short script. Make your program look for the data
file 'mydata.dat' and print the result on the screen (stdout), then
write the following script:

#!/bin/sh
# myprog.sh: run the same command on many different files
# usage: myprog.sh *.dat
for file in $* # for all parameters (e.g. *.dat)
do
# append the file name to result.dat
echo -n "${file}: " >> results.dat
# copy current argument to mydata.dat, run myprog
# and append the output to results.dat
cp ${file} mydata.dat ; myprog >> results.dat
done

Problem: I want to replace `geology' with `geophysics' in all my
text files. Shall I edit them all manually?

Solution: nope. Write this shell script:

#!/bin/sh
# replace $1 with $2 in $*
# usage: replace "old-pattern" "new-pattern" file [file...]
OLD=$1 # first parameter of the script
NEW=$2 # second parameter
shift ; shift # discard the first 2 parameters: the next are the file names
for file in $* # for all files given as parameters
do
# replace every occurrence of OLD with NEW, save on a temporary file
sed "s/$OLD/$NEW/g" ${file} > ${file}.new
# rename the temporary file as the original file
/bin/mv ${file}.new ${file}
done

Problem: I have some data files, I don't know their length and have to
remove their last but one and last but two lines. Er... manually?

12. Tips You Can't Do Without

Command completion: pressing <TAB> when issuing a command
will complete the command line for you. Example: you have to type
less this_is_a_long_name; typing in less thi<TAB>
will suffice. (If you have other files that start with the same
characters, supply enough characters to resolve any ambiguity.)

Back-scrolling: pressing SHIFT--PAG UP (the grey key) allows
you to backscroll a few pages, depending on your PC's video memory.

Resetting the screen: if you happen to more or cat
a binary file, your screen may end up full of garbage. To fix things,
blind type reset or this sequence of characters:
echo CTRL-V ESC c RETURN.

Pasting text: in console, see below; in X, click and drag to
select the text in an xterm window, then click the middle button
(or the two buttons together if you have a two-button mouse) to paste.

Using the mouse: ask your sysadm to install gpm, a mouse
driver for the console. Click and drag to select text, then right click
to paste the selected text. It works across different VCs.

13. Reading VMS tapes from Linux

(This section was written by Mike Miller)

13.1. Introduction

From time to time you may want to read tapes made on a VMS machine (or tapes
that are made to be readable by VMS and *nix systems). In general, this is
quite easy for DECFILES11A tapes.

Although you may be reading this as part of a Linux mini-HOWTO, I believe
that the information here is applicable to any *nix system - I've done this
on Linux, HP, Sun and DEC *nix systems. The main platform dependences that I
know are device names, which can differ on different systems, and the
options to mt for specifying the device name (for example, mt -f on Linux
and mt -t on HPUX 9).

13.2. The Basics

When reading a tape that has been made with the VMS ``copy'' command (or has
at least been made to look like it was made with copy) all you need to know
is there will be three files on the tape for each actual data file - a
header, the data, and a trailer. The header and trailer are interesting in
that they contain info on the file as it existed under VMS. The data is,
well, the data. Each of these files can be extracted from the tape with the
dd command. The tape can be positioned by skipping around with the mt
command.

Example: I've got VMS tape with a series of files on it. The first two were
originally named ce66-2.evt and ce66-3.evt on a VMS system. The tape label
is c66a2.

I'm left with six files: header1, data1, trailer1, header2, data2 and
trailer2. The syntax here is if="input file", bs="block size" and
of="output file". TAPE is expected to be a variable containing the device
name of your tape drive - for example, /dev/nts0 if you are using the first
SCSI tape on Linux.

If you wanted to read the second file, but not the first, you didn't care
about the header, and you wanted to use the original file name, do this:

Note the 4 - skip three files for the first file on the tape and one for the
next header. The second mt skips the second file's trailer and positions
the tape at the beginning of the next file - the third VMS header. You can
also use mt to skip backwards (bsf), rewind (rewind) and rewind and unload
the tape (offline, rewoffl).

13.3. Some details

The header and trailer files contain uppercase ASCII data used by VMS to
store file information such as block size. They also contain the file name,
which can be handy if you want to build scripts that automate read files or
search for a particular file. The first header on a tape volume is slightly
different than subsequent headers.

For a file that is the first file on the tape, as in header1 of the above
example, the first four characters will be "VOL1" followed by the volume
name. In the example, header1 starts with "VOL1C66A2". This is followed by
a series of spaces terminated with a numeral. After that is the string
"HDR1" which indicates that this is a file header. The characters
immediately following the HDR1 string are the VMS file name. In in the
example, this is "HDR1CE66-2.EVT". The next field is the volume name again.

For files that are not the first file on the tape, the initial VOL1 field is
not present. Other than that the header has the same structure as for the
initial file. Another useful field is the 7th field, which will end with
"DECFILES11A". This must be present on tapes that conform to the DEC
Files11A standard.

For full details on the header and trailer format, see the DEC FILES11A
documentation (on the orange/grey wall - ask your local VMS folks :-).

13.4. Comment on Block Size

In the example, I used a block size of 16k. On a *nix system, there is no
block size associated with a file on disk while, under VMS, each file has a
specific block size. That means that block size doesn't matter too much on
the Linux end... unless it makes it hard to read the tape. If you have
difficulty figuring out the block size and reading a tape, you can try
setting the hardware block size on your tape drive using `mt -f $TAPE setblk
0'. The exact form of the setblk option (and its availability) may depend
on the version of mt, the tape drive hardware interface and on your
particular flavor of *nix.

14. The End

14.1. Copyright

Unless otherwise stated, Linux HOWTO documents are copyrighted by their
respective authors. Linux HOWTO documents may be reproduced and distributed
in whole or in part, in any medium physical or electronic, as long as this
copyright notice is retained on all copies. Commercial redistribution is
allowed and encouraged; however, the author would like to be notified of any
such distributions.

All translations, derivative works, or aggregate works incorporating any
Linux HOWTO documents must be covered under this copyright notice. That is,
you may not produce a derivative work from a HOWTO and impose additional
restrictions on its distribution. Exceptions to these rules may be granted
under certain conditions; please contact the Linux HOWTO coordinator at the
address given below.

In short, we wish to promote dissemination of this information through as
many channels as possible. However, we do wish to retain copyright on the
HOWTO documents, and would like to be notified of any plans to redistribute
the HOWTOs.

If you have questions, please contact Tim Bynum, the Linux HOWTO
coordinator, at � via email.

14.2. Disclaimer

This work was written following the experience we had at the Settore di
Geofisica of the Universita' di Bologna (Italy), where a VAX 4000 has been
superseded and replaced by Linux-based Pentium PCs. Most of my colleagues
are VMS users, and some of them have switched to Linux.

``From VMS to Linux HOWTO'' was written by Guido Gonzato, �, and Mike Miller,
� who contributed the section on reading VMS tapes.
Many thanks to my colleagues and friends who helped me define the needs and
habits of the average VMS user, especially to Dr. Warner Marzocchi.

Please help me improve this HOWTO. I'm not a VMS expert and never will be,
so your suggestions and bug reports are more than welcome.